PROJECT SUMMARY The wide range of tobacco and nicotine products available ? and the lack of education on these products ? has likely has left the public confused about the relative harms of tobacco products, and nicotine more generally. The extent to which young adults conflate the harms of nicotine with the harms of tobacco use could have beneficial or harmful effects at the population level. Young people who believe that all nicotine and tobacco products are equally harmful and addictive may avoid tobacco use altogether, more readily use the more satisfying and harmful combusted products, or fail to pursue evidence-based nicotine medications to assist in quitting tobacco use. Existing studies on tobacco-harm perceptions are largely cross-sectional and NIH-funded research on tobacco harm perceptions has focused on the tobacco products themselves without addressing perceptions of nicotine separately. Given the new tobacco marketplace and various forms of nicotine available to today?s consumers, there is an immediate need to: 1) understand the interplay between nicotine harm perceptions and tobacco product harm perceptions; and, 2) how these perceptions affect susceptibility to use tobacco and nicotine-containing products and ultimately tobacco use patterns in the population as a whole. The proposed study harnesses secondary analyses in longitudinal data from a large, national sample of U.S. young adults (n = 4,100 young adults aged 18-34) with novel measures of nicotine harm perceptions to produce an in-depth examination of the perceived harm of nicotine, the relative harm of tobacco products, and the impact of these perceptions on tobacco-related intentions and behavior. Quantitative analyses will: 1) examine perceptions of nicotine and relative harm of tobacco products in a national sample of U.S. young adults and correlates of these perceptions (e.g., sociodemographics, tobacco use); 2) characterize young adult subgroups based on their perceptions of nicotine and relative harm of tobacco products using latent class analysis; and 3) describe the impact of nicotine and tobacco harm perception ?class? on longitudinal patterns in susceptibility and curiosity to use tobacco and tobacco use behavior. Findings from this study are of particular importance given the imminent implementation of a required warning label (?This product contains nicotine. Nicotine is an addictive chemical.?) on tobacco products covered by FDA. The scientific premise of this study is that a better understanding of perceptions of nicotine and tobacco products will guide the development of more informative and effective tobacco product warning labels and other public education efforts.